1. Field of the Invention
This invention pertains to capturing X-ray images and, more particularly, to an X-ray image capture element formed of a continuous photoconductive layer that converts a pattern of incident X-ray radiation into a pattern of electrical charges representative of the radiographic pattern. The photoconductive layer is formed over a two-dimensional array of solid state modules which capture the pattern of electrical charges and record digital representations of radiographic images.
2. Description of the Related Art
Although silver halide-based film systems are traditionally used in medical and industrial markets to capture patterns of X-rays that have been imagewise attenuated during passage through an object to be analyzed, non-film image capture systems are being introduced to reduce the time needed before radiograms are available and also to eliminate the expenses of film and processing. Scintillators and other X-ray sensitive devices have been used to convert the X-ray pattern into visible images that are converted into electrical signal patterns for subsequent enhancement, analysis, display and storage. More recently, systems have been developed to capture patterns of X-rays using solid state components, generally employing X-ray sensitive phosphors, intensifiers or photoconductive materials to convert X-ray patterns into electrical signal patterns. These systems generally involve converting an area X-ray image pattern into a corresponding array of electrical signals that are subsequently used to produce a visible display of the captured image. Most of these systems utilize converting apparatus formed from arrays of microelectronic devices that are produced with manufacturing processes whose yields are drastically reduced as the size of the array increases, Consequently, there are practical limitations to the maximum size of the captured X-ray image pattern. Hence solid state de,vices that capture X-ray patterns and produce electrical representations of the pattern cannot be readily produced in sizes large enough to capture the full size of popularly used X-ray imaging fields, for example, up to 14.times.17 inches as used to capture a chest X-ray.
Recent efforts to overcome this size limitation included assembling a large solid state X-ray sensor from a plurality of smaller solid state X-ray detectors which can be manufactured at reasonable yields. The use of such an assembly introduced a further problem, however, in that blind, non-radiation-detection areas are introduced at the borders of the individual detectors. These blind borders, between radiation detection areas, have been filled in by overlying smaller solid state radiation detectors, as described tier example in U.S. Pat. No. 5,105,087. In mother system, described in U.S. Pat. No. 4,873,708, a photodetector array having 14.times.17 inch dimensions is constructed by physically staggering 16 separate, electrically paired, modular charge-transfer devices in two rows such that the individual charge-transfer modules forming a row are aligned in an offset but overlapping positional relationship with respect to the next adjoining row. This array is scanned across the X-ray pattern to be captured using signal processing schemes to store and shift captured electrical signals between rows of charge-transfer devices until the signals exit the array for further processing. Older systems, like those described in U.S. Pat. No. 4,755,681, employ a plurality of separate radiation detectors and signal processing circuits arrayed in a two dimensional pattern having staggered joints between rows of the detectors to avoid a straight non-radiation-detection line. Shingle patterns and overlap patterns have also been used to produce an array of separate solid state radiation image detectors, as described in U.S. Pat. No. 4,467,342. These efforts are all directed at solving the problem of producing a large area radiation detector without introduction of non-radiation-detection or blind areas. None of the above prior art has suggested or recognized the advantage of eliminating the non-radiation-detection areas of an X-ray image capture element.